java - Can I define custom character class shorthands? -

java provides useful character classes \d , \w. can define own character classes? example, useful able define shorthands character classes [a-za-z_].

can define own character classes?

no, can't.

personally, when have (slightly) complicated regex, break regex in smaller sub-regexes , "glue" them string.format(...) this:

public static boolean isvalidip4(string address) {     string block_0_255 = "(0|[1-9]\\d|2[0-4]\\d|25[0-5])";     string regex = string.format(             "%s(\\.%s){3}",              block_0_255, block_0_255     );     return address.matches(regex); } 

which far more readable single pattern:

"(0|[1-9]\\d|2[0-4]\\d|25[0-5])(\\.(0|[1-9]\\d|2[0-4]\\d|25[0-5])){3}" 

note quick example: validating ip addresses can better done class java.net package, , if you'd that, pattern should placed outside method , pre-compiled.

be careful % signs inside pattern!